Technical Field
The present invention relates to a digital protective relay, and more particularly, a triple redundant digital protective relay and an operating method therefor.
Background Art
In general, protective relays are core devices for a health of a power system and are configured to analyze/monitor an operating state of a power system in real time and break a fault current flowing through a failed system by outputting a circuit breaker open signal immediately when a failure is detected, so as to prevent an electrical or mechanical failure of the power system from spreading to economical loss or unfortunate accident such as loss of precious human lives.
The most basic duty of such protective relays may be defined by operation sensitivity, selectivity, and speed. The operation sensitivity is an ability to recognize even a minimum failure, the selectivity is an ability to not misjudge a non-failure phenomenon as a failure, and the speed is an ability to operate as fast as possible so as to minimize a damage caused by a failure or spreading of the damage. Any one of them cannot be neglected.
If the protective relay fails to properly perform its operational duty, it may affect not only disruption of production or stoppage of work but also social disturbance, security, and the like. Until recently, blackouts occurred due to a series of malfunctions of relays in several countries including Korea. Since such blackouts are global issues and spread to economic and social problems, it is urgent that countermeasures be established.
In order to ensure the reliability of the protective relays that have to fulfill such important duties, it is compulsory to meet the safety and reliability standards presented by international standard bodies such as IEC, IEEE, and the like all over the world. In particular, the latest digital protective relays, which have been dominant since the 1980s, are devices manufactured based on highly-advanced high-precision/high-integration electronic technology, and standard specifications also tend to be reinforced with the times because the relays are sensitive to surge or noise and there are always the possibility of malfunction and incorrect operation during operation periods due to the deterioration of characteristics and rating caused by yearly variation.
However, since the test level defined in the specification is oriented toward generalization due to the attribute of the standard, it is hard to go beyond the basics. This can be seen from the fact that all the protective relays that have caused the large and small accidents of power systems until now were products certified as international standard.
In addition, recent digital protective relays have been expanded to such an extent that their function range has increased beyond comparison with the past due to the development of technology. Many functions of peripheral devices are integrated into the internal function of the protective relay, and thus, the whole system becomes simpler and more convenient. However, in practice, there is also a disadvantage that the failure of the multifunctional protective relay may deteriorate both reliability and functionality of the power system.
Even all the protective relay manufactures having a long history are constantly carrying out activities for reliability and quality improvement as well as functionality, based on many applications and experiences. This is an effort to comply with an increasingly extreme usage environment, but it is also a reality that the protective relays cannot be completely free from the risk and influence of internal failure. Therefore, there is always anxiety about the loss of life and property, occurrence of unnecessary opportunity costs, and the like. In particular, as can be seen in the case of Japan, since nuclear power plants have a great effect of failure, all major processes affecting safety are forced to use expensive products having a high safety grade.
As described above, there is a need to develop a technology that can significantly reduce the probability of failure and malfunction of protective relays and can increase the reliability of protective relays.